They owed, they owed, so to the post office they went Thousands rush to mail income tax forms and beat midnight deadline.

Thousands of taxpayers celebrated Procrastinator's Night yesterday -- an unofficial holiday marked by long lines in and around Baltimore's main post office in the crush to beat the midnight deadline for filing federal and state returns.

They came by car and truck, taxi and bus, motorcycle and 10-speed bike, some even walking on crutches, braving bumper-to-bumper madness on East Fayette Street, outside the only postal facility in the metropolitan area open until the Internal Revenue Service witching hour.

"When you owe, you always wait until the last minute," said Stanley V. Johnson, 32, an electrician and entrepreneur hunching over "Schedule A -- Itemized Deductions" on a glass display case in the post office lobby at 7:30 p.m. "It's like a ritual."

State and federal tax officials said the returns of about 500,000 of Maryland's 2.2 million taxpayers had not been received by yesterday morning -- and agreed that the number was not at all unusual.

"When you get down to April 14 or 15, what you have is the 20 or 25 percent of people who owe you money," said Marvin Bond, spokesman for the Maryland comptroller's office. "Most of those returns were done in February or March and they're just waiting for the deadline to write the check."

Many of the returns that were not yet done were being filled out last night in the post office lobby, however. Lines formed at the desks of federal and state income tax officials, on duty to help last-minute filers grapple with standard and not-so-standard deductions, earned income and unearned income, 401(k) and 1099G.

It was enough to cause a headache -- but no problem.

In fact, there was a dancing ibuprofen bottle on the Fayette Street sidewalk -- a guy in a costume helping a group of female co-workers hand out free headache pills.

Inside the pill-bottle outfit was 24-year-old Gary Martin, who got the job through a temporary employment agency. "They just asked me if I wanted to wear the costume," he said. "I thought it was a joke at first!"

It was no joke to 30-year-old Mark Dicus of "East Highlandtown," scribbling away on his tax forms, who had ridden his bicycle downtown to take part in the mad scene -- and found he had to pedal back home to pick up cash for a money order to pay his taxes.

Donald S. Johnson, a warehouse worker and free-lance inventor, blamed his plight on his employer for issuing a W-2 tax withholding statement in the name Sam Johnson. "I had to get that straightened out," said Mr. Johnson, whose middle name is Sam.

The ultimate procrastinators were those visiting the post office only to file for a four-month extension of the deadline.

"The IRS ran out of extension forms at 7:30 p.m.," said Roy Brewer, manager of main-office operations for the Postal Service. "We ran off 1,000 more on the copier."

Domenic LaPonzina, an IRS spokesman, said tax procrastinators fall into four main excuse categories: those "legitimately up against the wire" because of illness or paperwork snafus; habitual last-minute filers who also renew car license tags on the last day or write term papers the night before they are due; those who "do it as a ritual, just to be able to say they filed on April 15"; and those who owe money.

Stanley Johnson seemed to fall into several of those categories, owing money and "like a ritual" showing up at the post office every April 15 to do his taxpaying duty.

"I've been cramming all my life," he said.

"But I am getting earlier. Last year I came about 9 p.m., and didn't get out of here until 10:30 or 11."

For many Marylanders who filed early and had overpaid their taxes, refunds have already been mailed: 992,000 state checks averaging $355 each and 1.2 million federal checks averaging $1,100.